This application claims the benefit of Korean Patent Application No. 2001-60143, filed Sep. 27, 2002, in the Korean Intellectual Property office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fusing device of an electrophotographic image forming apparatus, and more particularly, to a fusing device of an electrophotographic image forming apparatus having a fusing roller and end caps securing an electric connection between a heater supplying heat to the fusing roller and a power supply device coupled to the heater.
2. Description of the Related Art
FIG. 1 is a schematic perspective view of a conventional electrophotographic image forming apparatus. Referring to FIG. 1, the conventional electrophotographic image forming apparatus includes a paper ejecting unit 1, an operating unit 2, a control board cover 3, an upper cover opening button 4, a paper display window 5, a multi-purpose feeding window 6, a paper cassette 7, an option cassette 8, and an auxiliary stand 9.
FIG. 2 is a schematic cross-sectional view of a fusing device 10 of a conventional electrophotographic image forming apparatus employing a halogen lamp as a heat source.
Referring to FIG. 2, the conventional fusing device 10 includes a cylindrical fusing roller 11 and a heater 12, e.g., the halogen lamp, installed in an interior center portion of the fusing roller 11.
A coating layer 11a, such as Teflon, is coated on a surface of the fusing roller 11. The heater 12 generates heat from an interior portion of the fusing roller 11, and the fusing roller 11 is heated by a radiant heat emitted from the heater 12.
FIG. 3 is a longitudinal cross-sectional view illustrating a relationship between the fusing roller and a pressure roller of the conventional electrophotographic image forming apparatus employing the halogen lamp as the heat source as shown in FIG. 2.
Referring to FIG. 3, a pressure roller 13 is disposed to face a sheet of paper 14 at a lower portion of the fusing device 10. The pressure roller 13 is elastically supported by a spring 13a to press the paper 14 passing between the fusing roller 11 and the pressure roller 13 with a predetermined pressure. A powdered toner image 14a is formed on the paper 14 and is pressed with a predetermined pressure and heated by heat when the paper 14 passes between the fusing roller 11 and the pressure roller 13. In other words, the toner image 14a is fused and fixed on the paper 14 by the heat of the fusing roller 11 and pressure of the pressure roller 13.
A thermistor 15 measuring a surface temperature of the fusing roller 11 and a thermostat 16 cutting off a power supply of the heater from an external power source when the surface temperature of the fusing roller 11 exceeds a predetermined set value, are provided at one side of the fusing roller 11. The thermistor 15 measures the surface temperature of the fusing roller 11 and transmits an electric signal corresponding to the measured temperature to a controller (not shown) of a printer (not shown). The controller controls a quantity of electricity supplied to the halogen lamp 12 according to the measured temperature to maintain the surface temperature of the fusing roller 11 within a given range. When the surface temperature of the fusing roller 11 exceeds the predetermined set value because the thermistor 15 and the controller fails in controlling the surface temperature of the fusing roller 11, a contact (not shown) of the thermostat 16 becomes open to cut off the power supply of the halogen lamp 12 from the external power source.
The conventional fusing device 10 using the halogen lamp 12 as the heat source unnecessarily consumes a large amount of electric power. Particularly, when power is turned on, the conventional fusing device 10 requires quite a long warming-up time. The warming-up time may range from several tens of seconds to several minutes. In addition, in the conventional fusing device 10, since the fusing roller 11 is heated by radiation emitted from the heat source 12, heat transmission is slow, and compensation for a temperature deviation caused by a decrease in temperature occurring due to a contact with the paper 14 is slow. As a result, it is difficult to maintain the surface temperature of the fusing roller 11 constant. Moreover, since the electric power must be periodically supplied to the heat source 12 in order to maintain the surface temperature of the fusing roller 11 constant in a standby mode in which an operation of the printer is in pause, unnecessary electric power is consumed. A considerable time is required to convert the standby mode into an operation mode for an image output, thereby making it difficult to achieve a fast image output.
FIG. 4 is a cross-sectional view of another conventional fusing device 200 employed in the electrophotographic image forming apparatus.
Referring to FIG. 4, a heating plate 22 is provided at the inner bottom portion of a flexible, cylindrical film tube 21. A pressure roller 23 is disposed to face the heating plate 22, and the paper 14 is disposed therebetween.
The film tube 21 is rotated by a separate rotating device. Locally heating a portion of the heating tube 21 disposed between the heating plate 22 and the pressure roller 23 consumes a low power, but this method is difficult to be applied to fast printing.
In order to solve the above problem, fusing devices adopting a heat pipe capable of instantaneously heating the fusing devices by a high heat conductivity and having a low power consumption characteristic are disclosed in Japanese Patent publication Nos. Hei 6-348176, Hei 11-282294 and 2000-25976.
In the fusing devices adopting the heat pipe, a heat source is arranged at one portion of a fusing roller, the portion deviating from a fusion area. If the heat source is arranged in such a manner, an overall size of the fusing device may increase. Thus, it is necessary to solve another problem of a structural complexity.
Fusing devices having a heat source incorporated into a fusing roller as disclosed in Japanese Patent publication Nos. Showa 60-55368, Hei 4-335691, Hei 4-360185, Hei 8-171301, Hei 8-262905, Hei 8-305195 and Hei 9-90811, do not encounter an increased structural complexity. However, since these fusing devices have a plurality of heat pipes locally disposed in the fusing roller, a manufacturing process becomes very complex. Also, since the heat pipes are locally disposed in the fusing roller, there is a temperature difference between portions among adjacent heat pipes and portions contacting the heat pipes.
According to a method in which a heat-generating resistive coil is inserted into the heat pipe, power supply portions disposed at both ends of the heat-generating resistive coil are electrically and thermally weak.
In particular, since insulating caps at both ends of the fusing roller are complex in view of shape and structure, an insulation of the insulating caps ensuring durability thereof is difficult to achieve. In addition, due to limitations of a heat-generating resistive element used in the fusing device in view of a voltage withstanding characteristic and a voltage application range, special materials should be used, causing a high manufacture cost.
To solve the above and other problems, it is an object of the present invention to provide a fusing device of an electrophotographic image forming apparatus with improved end caps establishing a stable electrical connection between a power supply and a heater.
Additional objects and advantageous of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the object of the present invention, there is provided a fusing device of an electrophotographic image forming apparatus. The fusing device includes a tubular internal pipe sealed at its ends to maintain a predetermined internal pressure to accommodate a predetermined amount of a working fluid in its inner space, a heater installed to wrap the internal pipe to generate heat, a power supply unit electrically connected to the heater to supply an external power to the heater, a cylindrical roller installed to wrap the heater, and end caps installed at both ends of the cylindrical roller, wherein each end cap includes a large-diameter portion in which an electrode electrically connected to the power supply unit is to be installed, and a small-diameter portion fittingly fixed to the end of the cylindrical roller by a locking unit.